1. Field of the Invention
The present invention generally relates to a photosensitive electrochromic device.
2. Description of Related Art
A regular electrochromic device may serve as a smart window for power saving and be used in green buildings, but it still requires an electric energy source, which consumes energy. Typical electrochromic devices are categorized into a solid type and a liquid type. A solid electrochromic device has a structure as shown in FIG. 1, where an upper layer and a lower layer of an electrochromic device 100 are respectively formed by a glass/plastic transparent substrate 102. There are at least five coated/deposited layers with different functions disposed between the two transparent substrates 102, and the five layers are, for example, two transparent conductive layers 104, an electrochromic layer 106, an electrolyte layer 108 and an ion storage layer 110, which are sandwiched into a combination to form a structure similar to a battery.
FIG. 2 is a structural view of a conventional liquid-type electrochromic device, wherein a device 200 is constituted of two transparent conductive substrates 202. Generally, one of the transparent conductive substrates 202 contains a transparent substrate 204 and an anode 206, and the other contains the transparent substrate 204 and a cathode 206 opposite to the anode 206. An electrochromic solution 208 is disposed between the two transparent conductive substrates 202 and includes an organic small molecule electrochromic material and an electrolyte solution.
Due to the increasing energy-saving consciousness, a novel building integrated photovoltaics (BIPV) system implemented by combining solar cells and electrochromic devices has been developed, which has become a new tendency nowadays. With BIPV system, no additional power is needed to automatically adjust the color shade of windows with electrochromic glass according to the variation of indoor and outdoor luminance, which has great advantages in reducing indoor heat to achieve energy-saving purpose.
The present invention is directed to a photosensitive electrochromic device, in which an employed silicon thin-film solar cell module serves as an element of the device converts light energy into electric energy for color changing, so as to suit green energy-saving purposes. When combined with specifically designed switches, the photosensitive electrochromic device can supply electric current to AC electrics and DC electrics through connection with a DC/AC converter and a DC charge storage apparatus, which provides a new power source under the present energy crisis.
So far, the development of photoelectrochromic device relies on dye sensitive solar cells for generating electric power. U.S. Pat. No. 6,369,934B1 disclosed an all-organic multi-layer photoelectrochemistry device. However, to apply a typical structure like this in practice, many problems need to be solved, for example, the stability of the employed photosensitive layer or the feasibility of enlarging the area of the device.
U.S. Pat. No. 5,377,037 provides a design that combines a solar cell and an electrochromic device into a single device, wherein on a first conductive glass substrate, a silicon thin-film solar cell module and an inorganic electrochromic device are disposed in tandem arrangement and combined into one element. The element faces the second transparent conductive substrate on the opposite side and a liquid organic electrolyte solution or a solid inorganic electrolyte layer is disposed between the two elements. However, the inorganic electrochromic material intrinsically requires a high driving voltage and a high charge density for working, and thus the thickness of the intrinsic layers of the silicon thin-film solar cells can not be reduced, which leads to a lower contrast given by the device and becomes a barrier for its application in the smart window.
U.S. Pat. No. 5,805,330 provides an all-organic structure, wherein both an upper layer and a lower layer are transparent conductive substrates, and an organic small molecule electrochromic material and an electrolyte solution are disposed therebetween. A solar cell module adheres to the edge of the electrochromic glass, so that when illuminated by sunlight, the current generated by the solar cell is supplied to the electrochromic device via an output terminal of the cell and the electrochromic device thereby changes color.
U.S. Pat. No. 6,055,089 provides an electrochromic system that combines a solar cell with an electrochromic device, wherein an inorganic electrochromic glass is disposed in front of a silicon crystal solar cell module, and a layer of air is between the inorganic electrochromic glass and the silicon crystal solar module. Under sunlight irradiation, electricity generated by the solar cell is outputted to the electrochromic device via terminals of the cell so as to change the color of an electrochromic layer. The color contrast within the electrochromic system controls the incident light intensity falling on solar cell and thereby determines the output current of the solar cell.
Although electrochromic technology has been researched and developed for many years, so far only electrochromic rear-view mirror has been massively commercialized, and other types of large-area electrochromic devices still encounter the problem of non-uniform change of color, also called iris effect, which phenomenon is illustrated in FIG. 3. Referring to FIG. 3, it is noted that, in a planar structure 300 provided by the above-mentioned patents, the path lengths of electric fields at the periphery (where the electrode 302 is located) and the center area 304 of the employed electrodes 302 are different from each other, which leads to variation in the impedances, and results in significant difference in color concentration between the periphery (where the electrode 302 is located) and the center area 304.